A massive MIMO systems scales up conventional MIMO systems by possibly orders of magnitude, i.e., hundreds of antennas at a Base-Station (BS) to simultaneously serve tens of User Equipments (UEs) in the same time-frequency resource. Such a system may provide tremendous advantages [1]-[3]. With the capabilities of aggressive spatial multiplexing and great array gains, a massive MIMO system may achieve capacity increase and energy efficiency improvement simultaneously. In addition, it can be built with inexpensive and low-power components. It also has the potential to significantly reduce the latency of the air interface, simplify the media-access layer, as well as increase the robustness to both unintentional artificial interference and intended jamming. In general, massive MIMO systems are considered in Time Division Duplex (TDD) mode, taking advantages of the channel reciprocity between the uplink and downlink, although Frequency Division Duplex (FDD) is also possible as in [4], or our patent application PCT/US14/71752.
In a massive MIMO system, a BS selects users at each scheduling Transmission Time Interval (TTI) and communicates with them in the same FR. Different precoding algorithms for the downlink and decoding algorithms for the uplink could be employed at each TTI, e.g., Conjugate Beamforming (CB) or Zero-Forcing Beamforming (ZFB) for the downlink and Maximal-Ratio Combining (MRC) or Zero-Forcing Decoding (ZFD) for the uplink. Since the UEs associated to a BS have different channel conditions, it is advantageous to divide UEs into different groups based on their channel conditions and then allocate the FR to each group. However, a proper UE grouping and FR allocation strategy is currently lacking for massive MIMO systems. Prior arts put users of diverse channel conditions in the same FR, and may suffer significant loss of sum capacity and/or reduction of data rate of UEs with excellent channel conditions to accommodate UEs with bad channel conditions.
This invention presents embodiments that provide a strategy for UE grouping and FR allocation in massive MIMO systems.